Process For Nitroalkane Recovery By Aqueous Phase Recycle To Nitration Reactor

ABSTRACT

Disclosed are a process and an apparatus for synthesizing nitroalkanes by reaction of a hydrocarbon feedstock with aqueous nitric acid. Energy and capital costs may be reduced by recycling a majority of the aqueous phase back to the reactor.

FIELD

The invention relates to a process for synthesizing nitroalkanes. Morespecifically, the invention relates to a process for improvednitroalkane recovery in which an aqueous phase is recycled back to thenitration reactor.

BACKGROUND

The nitration of hydrocarbons generally involves the distillation ofboth an oil phase and an aqueous phase. However, this process requireslarge energy and capital expenditures.

In conventional vapor phase nitration schemes, described in U.S. Pat.Nos. 3,780,115 and 3,869,253, the reactor effluent is rapidly quenchedand the quenched mixture is sent to a separator. The gas phase is thenwithdrawn for purification and recycling and the aqueous phase and theoil phase are separated by decantation and treated simultaneously torecover the desired nitroparrafin by distillation. New high pressurephase nitration processes use a lower strength nitric acid, resulting ina larger aqueous phase. Processing both the large aqueous phase and theoil phase is very energy-consuming. A need exists, therefore, for moreeconomical and energy efficient processes for the manufacture ofnitroalkanes.

BRIEF SUMMARY

In one aspect, a process is provided for synthesizing at least onenitroalkane. The process comprises: reacting a hydrocarbon feedstockwith aqueous nitric acid in a reactor at a reactor pressure and areaction temperature, such that a product stream comprising nitratedcompounds and byproducts is formed; separating the product stream intoat least an oil phase, a gas phase, and an aqueous phase, wherein theoil phase and the aqueous phase contain nitrated compounds; dividing theaqueous phase into a first aqueous stream and a second aqueous stream;returning the first aqueous stream to the reactor; and recovering the atleast one nitroalkane from at least one of the oil phase and the secondaqueous stream.

In another aspect, a process for synthesizing at least one nitroalkanecomprises: reacting a hydrocarbon feedstock with aqueous nitric acid ina reactor at a reactor pressure and a reaction temperature, such that aproduct stream of nitrated compounds and byproducts is formed; quenchingthe product stream to separate the product stream into at least an oilphase, a gas phase, and an aqueous phase; dividing the aqueous phaseinto a first aqueous stream and a second aqueous stream; returning thefirst aqueous stream to the reactor; absorbing oil-soluble andwater-soluble components from the gas phase into the oil phase and thesecond aqueous stream, respectively, to form a gas-recovered mixture;separating a gas-recovered aqueous phase from the gas-recovered mixture;and recovering the at least one nitroalkane from at least one of the oilphase and the second aqueous stream.

In yet another aspect, an apparatus for synthesizing at least onenitroalkane is provided. The apparatus comprises: a reactor for reactinga hydrocarbon feedstock with aqueous nitric acid to produce a reactionproduct stream; a cooling system for quenching the reaction productstream such that it phase separates into at least a gas phase, an oilphase, and an aqueous phase; a divider for dividing the aqueous phaseinto a first aqueous stream and a second aqueous stream; a recyclingsystem for returning the first aqueous stream to the reactor; and arecovery system for recovering the at least one nitroalkane from atleast one of the oil phase and the second aqueous stream.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the apparatus for synthesizing at leastone nitroalkane, in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

As noted above, in one aspect a process for synthesizing at least onenitroalkane is provided. One important advantage of this process is thatit can recycle a majority of the aqueous phase as nitric acid diluent inthe reactor without additional processing. The recycle may occurimmediately after a reactor product stream is divided into an oil phase,a gas phase, and an aqueous phase. The solubility of nitropropanes(2-nitropropane and 1-nitropropane) in water is low and nitropropanesare significantly less reactive than propane. Thus, the presence of2-nitropropane (in low concentration) in the aqueous phase returned toreactor does not affect the reactor performance significantly.

FIG. 1 illustrates an apparatus 100 for synthesizing at least onenitroalkane. A hydrocarbon feedstock 101 and aqueous nitric acid 102 maybe introduced into a reactor 103. The hydrocarbon feedstock 101 and theaqueous nitric acid 102 may react at a reactor pressure and a reactiontemperature, such that a product stream 104 comprising nitratedcompounds and byproducts may be formed.

The hydrocarbon feedstock 101 and the aqueous nitric acid 102 may bemixed, or partially mixed, prior to entry into the reactor 103 or,alternatively; they may be added individually, with mixing to occurwithin the reactor 103. In addition, hydrocarbon feedstock 101 and theaqueous nitric acid 102, whether added together or individually, may bepreheated prior to entry into the reactor 103.

In one example, the hydrocarbon feedstock 101 may consist essentially ofpropane and acetic acid. In other examples of the hydrocarbon feedstock101 may include, without limitation, one or more of the following:alkanes and cycloalkanes (including alkyl substituted cycloalkanes),such as propane, isobutane, n-butane, isopentane, n-pentane, n-hexane,n-heptane, n-octane, 2,3-dimethylbutane, cyclohexane, cyclopentane, andmethylcyclohexane; aryl alkanes such as ethylbenzene, toluene, xylenes,isopropyl benzene; 1-methylnaphthalene and 2-methylnaphthalene and4-methylbiphenyl; fused cycloalkanes; alkyl substituted fused arylcompounds; fused cyclolalkane-aryl compounds (including alkylsubstituted derivatives), such as tetralin, decalin, andmethylnaphthalene; and carboxylic acids, such as acetic acid, propanoicacid, butanoic acid, and hexanoic acid. The nitration of reactants thatalready have one or more nitro substituents may also be contemplated,provided that the reactant still has an available hydrogen.

The aqueous nitric acid 102 may be delivered to the reactor 103 in theform of an aqueous solution that contains at least about 10 weightpercent, preferably at least about 15 weight percent, more preferably atleast about 20 weight percent, of the acid. Further, the solution maycontain less than about 50 weight percent, preferably less than about 40weight percent, and more preferably less than about 35 weight percent,of the acid. In other embodiments, the nitric acid solution may containbetween about 15 and about 40 weight percent of the acid. In furtherembodiments, the nitric acid solution may contain between about 18 andabout 35 weight of the acid.

The mole ratio of the hydrocarbon feedstock 101 to the aqueous nitricacid 102 may be at least about 0.3:1, more preferably at least about0.5:1.

The reactor pressure may be at least about 500 psi (34 atm), morepreferably at least about 1000 psi (68 atm), and further preferably atleast about 1200 psi (82 atm). In some embodiments, the pressure may beabout 1600 psi (109 atm) or less, preferably about 1500 psi (102 atm) orless, more preferably about 1400 psi (95 atm) or less. In otherembodiments, the pressure may between about 1000 psi (68 atm) and 1400psi (95 atm). Various methods known in the art may be used formaintaining the pressure within the desired range including, forexample, through the use of a back-pressure regulator.

The reaction temperature within the reactor may be controlled (forexample with heat exchange fluid or using heat generated from thereaction) to at least about 140 degrees Celsius and to less than about325 degrees Celsius. In other embodiments, the temperature may be atleast about 215 degrees Celsius and to less than about 325 degreesCelsius. In some embodiments, the temperature may be at least about 180degrees, at least about 200 degrees, at least about 230 degrees, or atleast about 240 degrees. In other embodiments, the temperature may beless than about 290 degrees, less than about 280 degrees, less thanabout 270 degrees, or less than about 250 degrees. In furtherembodiments, the temperature may be between about 200 and 250 degreesCelsius. In yet further embodiments, the temperature may be betweenabout 215 and 280 degrees Celsius, or between about 220 and 270 degreesCelsius.

The residence time of the reactants in the reactor 103 may be preferablyat least about 30 seconds, more preferably at least about 90 seconds.Residence time may be controlled in various ways including, for example,by the length and/or width of the reactor or through the use of packingmaterial. Residence time may be determined by dividing the volume of thereactor by the inlet flow rates.

The reactor 103 may be a downflow configured reactor. That is, thereactor, which is preferably of an elongated and linear shape, such as atube shape, may be positioned so that reactants are added through anentry port at or near the top of the reactor and then flow down thereactor for a residence time that is sufficient to allow reaction tooccur and formation of the desired product. The product mixture may becollected through an exit port at or near the bottom of the reactor.

The operation of the reactor in a downflow configuration providescertain advantages over prior art systems, which generally utilize ahorizontal, upflow, coiled or a batch autoclave type apparatus. Inparticular, the downflow configuration of the invention providesnitrated compounds that contain relatively low levels of oxidationbyproducts as compared to such prior art systems.

Without wishing to be bound by any particular theory, it is believedthat the advantages of the downflow reactor result primarily from itsability to minimize the amount and residence time of the liquid phasewithin the reactor. The liquid phase in general contains a low moleratio of hydrocarbons to nitric acid. This low mole ratio favorsoxidation chemistry at the expense of nitration and oxidation thereforeprimarily occurs in the liquid phase. In a downflow reactor (alsoreferred to as a trickle bed reactor) the gas is the continuous phaseand the liquid trickles down the reactor walls or packing. Therefore,the amount of liquid phase(s) in a downflow configured reactor ismaintained at a low level and consequently oxidation chemistry isminimized.

In contrast, in an upflow reactor, also referred to as a bubble column,the liquid is the continuous phase (and bubbles rise quickly through thecontinuous liquid phase). Thus, an upflow reactor maximizes the liquidholdup. Because, as noted above, oxidation primarily occurs in theliquid phase, the upflow reactor maximizes the formation of oxidationbyproducts. Similarly, coil and horizontal reactor configurations alsoincreases liquid residence time and therefore oxidation chemistry ascompared to a downflow reactor. A further disadvantage of coiledreactors is that they are not well-suited for industrial scaleproduction because of the difficulty of fabricating large scale reactorsin this shape.

The reactor 103 may also be packed with a packing material to improvereactant mixing and heat transfer and/or to vary the reactor volume.Packing of the reactor may be preferred, for example, in a propanenitration system where it is desired to increase the concentration of2,2-dinitropropane in the product stream. Suitable packing materials mayinclude, for example, glass beads, random packing, or structuredpacking, such as those typically employed in distillation devices. Otherpacking materials are known in the art and may be used. The reactor 103may also be an un-packed reactor.

The product stream 104 then may enter a first cooling system 105. In thefirst cooling system 105, the product stream 104 may be quenched suchthat it separates into at least a gas phase 106, an oil phase 107, andan aqueous phase 108. One or more of the gas phase 106, the oil phase107, and the aqueous phase 108 may contain nitrated compounds. Theaqueous phase 108 then may enter a divider 109, which may divide theaqueous phase 108 into a first aqueous stream 110 and a second aqueousstream 111. The divider 109 may include at least one flow-meter tocontrol the amount of the aqueous phase 108 in the first aqueous stream110 and the second aqueous stream 111. The first aqueous stream 110 maythen enter a recycling system 112. The recycling system 112 may mix thefirst aqueous stream 110 with the aqueous nitric acid 102 such that thefirst aqueous stream 110 dilutes the aqueous nitric acid 102 prior toentering the reactor 103. About 65 to 85 percent of the aqueous phase108 may be returned to the reactor 103 through the recycling system 112.In an illustrative embodiment, a highly favorable energy and capitalbenefit may be obtained by returning 80 percent of the aqueous phase 108to the reactor 103.

Further processing, such as distillation, may be carried out on the gasphase 106, the oil phase 107, and the second aqueous stream 111 torecover the at least one nitroalkane. For example, the gas phase 106,the oil phase 107, and the second aqueous stream 111 may enter arecovery system 113 for recovering the at least one nitroalkane from atleast one of the oil phase 107 and the second aqueous stream 111. Therecovery system 113 may comprise an absorber 114, a separator 117, and astripping apparatus 120. The gas phase 106, the oil phase 107, and thesecond aqueous stream 111 may enter the absorber 114 for absorbingwater-soluble and oil soluble components from the gas phase 106 into theoil phase 107 and into the second aqueous stream 111 to form ahydrocarbon gas stream 115 and a first gas-recovered mixture 116. Thefirst gas-recovered mixture 116 may enter the separator 117, forseparating a gas-recovered aqueous phase 118 from the firstgas-recovered mixture 116 to form a second gas-recovered mixture 119.The at least one nitroalkane may be recovered from either the secondgas-recovered mixture 119 or the gas-recovered aqueous phase 118 orboth. The at least one nitroalkane may be 2-nitropropane,2,2-dinitropropane, or 1-nitropropane.

In an illustrative embodiment, the gas-recovered aqueous phase 118 mayalso be introduced into a stripping apparatus 120 to recover the atleast one nitroalkane. The stripping apparatus 120 may divide thegas-recovered aqueous stream into at least a first top product 121 and afirst bottom product 122. The first top product 121 may be introducedinto a second cooling system 123 to provide at least a second topproduct 124 and a second bottom product 125. The second top product 124may then be introduced into a third cooling system 126 to provide atleast a third top product 127 and a third bottom product 128. The secondbottom product 125 and the third bottom product 128 may be combined toform a fourth bottom product 129. The fourth bottom product 129 mayenter a fourth cooling system 130 to produce at least a fourth topproduct 131, a middle product 132, and a fifth bottom product 133. Thefourth top product 131 may combine with third top product 127 to form afifth top product 134. The middle product 132 may combine with thesecond gas-recovered mixture 119 to produce a third gas-recoveredmixture 135. The third-gas recovered mixture 135 may contain at leastone nitroalkane, for example, 2-nitropropane, 2,2-nitropropane, or1-nitropropane. The fifth bottom product 133 may be combined with thegas-recovered aqueous phase 118 and may be introduced into the strippingapparatus 120.

According to one embodiment, propane is reacted with aqueous nitric acidto form 2-nitropropane and other nitrated paraffins under the specificprocess conditions described herein. The reaction of propane with nitricacid may be carried out in a corrosion resistant reactor, such as atitanium reactor. The reactor is optionally surrounded by a shell withinput and output ports for feeding a heat transfer fluid to the reactor.The heat transfer fluid, which can be, for example, an oil, allows thetemperature of the reaction to be controlled to within the desiredparameters.

It should be noted, however, that because the reaction between thenitric acid and propane is exothermic, use of a shell and a heattransfer fluid are not required. The temperature of the reaction can beregulated to be within the desired parameters by simply regulating theaddition rate and/or concentration of the reactants.

EXAMPLES

Various examples are demonstrated using a computer simulation (forExamples 1 and 2) and a lab scale reactor (for Example 3 and 4).

The lab scale reactor is a single tube shell-and-tube heat exchangerwith a thermowell located axially down the center of the reactor inorder to determine the temperature profile along the reactor's length.The reactor is 46″ long and has a shell which is 1.25″ OD 304 stainlesssteel with a ½″ OD (0.37″ ID) type 2 titanium process tubing and a ⅛″ OD(0.093″ ID) type 2 titanium thermowell. A very fine, movablethermocouple is inserted into the thermowell for the temperature profilemeasurement. The thermowell can be removed and the reactor filled withpacking. The reactor is mounted vertically. The nitric acid and propanereactant streams are mixed in a Swagelok® “T” fitting at roomtemperature prior to entering the reactor. Hot oil is fed to the reactorshell countercurrent to the reactants. The reactor effluent (reactionproduct) is cooled in a shell-and-tube heat exchanger using water as thecoolant. The effluent is then depressurized with the gases and liquidscollected, measured, and analyzed.

In Examples 3 and 4 below, the mass balance of the nitration reaction isdetermined by GC/MS for gases, aqueous, nitroparaffin oil, and scrubberliquids, Karl Fisher titration for water content, potentiometrictitration for strong/weak acid quantification, and HPLC for weak acididentification and quantification.

Metrics shown in the Tables below are calculated as follows:

Nitric Acid conversion(%)=100×(Nitric Acid in−Nitric Acid out)/NitricAcid in;

Propane conversion(%)=100×(Propane in−Propane out)/Propane in;

Nitric Acid yield=g nitric acid consumed/g nitroparaffins formed;

Organic yield=g propane and acetic acid consumed/g nitroparaffinsformed;

1-nitropropane selectivity(%)=100×g 1-nitropropane/g nitroparaffinsformed;

2-nitropropane selectivity(%)=100×g 2-nitropropane/g nitroparaffinsformed;

Nitromethane selectivity(%)=100×g nitromethane/g nitroparaffins formed;

Nitroethane selectivity(%)=100×g nitroethane/g nitroparaffins formed.

Grams of nitric acid consumed is calculated by subtracting the moles ofnitric oxide in the reaction product from the moles of nitric acid inthe feed and then converting the number of moles to grams using themolecular weight of nitric acid.

Grams of nitroparaffins include: nitromethane, nitroethane,1-nitropropane, and 2-nitropropane.

Example 1 Nitration Scheme without Aqueous Recycle

Propane is nitrated using 30 weight percent dilute aqueous nitric acidas the nitrating agent at the following process conditions: 1380 psireactor pressure, 281.6 degrees Celsius reactor temperature, a residencetime of 120 seconds, and a propane to nitric acid mole ratio of 1.5:1. Acomposition of a typical product stream from the reactor is summarizedin Table 1.

TABLE 1 Reactor product stream composition Temperature 281.6° C.Pressure 94 atm Mass Component fraction Water 0.682 Carbon monoxide0.008 Nitrogen 0.004 Nitric oxide 0.028 Nitrous oxide 0.006 Propane0.102 Carbon dioxide 0.016 Acetone 0.002 Acetic acid 0.049 Nitromethane0.001 Nitric acid 0.019 Nitroethane 0.001 Propionic acid 0.0062-nitropropane 0.067 1-nitropropane 0.006 2,2-dinitropropane 0.003

The product stream is then quenched in an after-cooler to about 38degrees Celsius and subsequently flashed into a gas phase, an aqueousphase, and an oil phase. The aqueous phase comprises almost all of thewater along with the organic acids and the oil phase comprises thenitroalkanes along with propane and acetone. The aqueous/oil phasepartition coefficients for the constituting species are given in Table2.

TABLE 2 Aqueous/oil phase partition coefficients at 48° C. and 94 atmComponent K_(aqu/oil) Water 91.517 Carbon monoxide 0.076 Nitrogen 0.032Oxygen 2.377 Nitrous oxide 0.037 Propane 0.007 Carbon dioxide 23.069Nitrogen dioxide 1.713 Acetone 0.107 Acetic acid 0.348 Butane 0.216Nitromethane 0.118 Nitric acid 177.820 Nitroethane 0.032 Propionic acid0.125 2-nitropropane 0.009 1-nitropropane 0.003 2,2-dinitropropane 0.002

The gas phase, the aqueous phase, and the oil phase are then fed to anabsorber, where the gas phase is steam stripped using medium pressuresteam and the un-reacted propane and gas by-products are routed via thecolumn overheads to the propane recovery section. The oil phase isabsorbed in the aqueous phase and the resulting stream from the absorberis fed into a nitro-paraffin recovery column. The absorber is operatedat a pressure of 147 psi (10 atm), equivalent to the operating pressureof the downstream propane recovery column. The nitro-paraffin recoverycolumn is operated at a pressure of 22 psi (1.5 atm), where almost allthe nitro-paraffins (along with around 3000 lb/h water) are obtained asoverheads. The bottom stream from the nitro-paraffin recovery column isessentially water and dissolved acetic, propionic, and nitric acid. Thisstream, after exchanging heat with the resulting stream from theabsorber, is then sent to intermediate water storage from where it isrecycled as nitric acid diluent. The top stream from the nitro-paraffinrecovery column containing nitroparaffins, water and non-condensables,is then routed through a series of cooler-decanter units, to condenseand segregate nitroparaffins which are then sent to the nitropropanerecovery section. The residual water recovered from the top stream isrecycled back to the nitro-paraffin recovery column. A small amount ofpropane is recovered in the top stream of the nitro-paraffin recoverycolumn. The resultant gas stream contains ˜10 lb/h 2-nitropropane whichis recovered in the tail-gas column by scrubbing with recycle water. Thetop stream from the tail-gas column is compressed to a pressure of 147psi (10 atm) and routed to the propane recovery section. The aqueousscrubbing solution from the tail-gas column is recycled back to theabsorber.

This high pressure process uses 15-30% dilute nitric acid. The nitrationprocess generates around 3700 lb/h water which in addition to that usedfor nitric acid dilution amounts to water mass of ˜52000 lb/h. Theaqueous stream composition is given in Table 3.

TABLE 3 Aqueous stream composition Temperature 49° C. Pressure 94 atmMass Component fraction Water 0.889 Carbon monoxide 404 ppm Nitrogen 160ppm Nitric oxide 218 ppb Nitrous oxide 0.002 Propane 0.009 Carbondioxide 0.013 Acetone 0.002 Acetic acid 0.045 Nitromethane 0.001 Nitricacid 0.029 Nitroethane 222 ppm Propionic acid 0.003 2-nitropropane 0.0081-nitropropane 223 ppm 2,2-dinitropropane 66 ppm Methane 2 ppm

Example 2 Nitration Scheme with Aqueous Recycle

In an illustrative embodiment, at approximately the same processconditions as in Example 1, 75-85 percent of the aqueous stream comingout of the post-reactor flash is recycled to the nitration reactor asnitric acid diluent. The oil phase is cooled to 16 degrees Celsiusbefore feeding to the absorber to reduce loss of nitropropanes in theoverhead. The gas stream is steam stripped of all volatiles at apressure of 44.1-73.5 psi (3-5 atm) and the resulting stream, which isessentially un-reacted propane and gas byproducts, is then compressed toa pressure of 147 psi (10 atm) in a two-stage compressor before routingit to the propane recovery section. The bottom stream from the absorberis cooled and phase-separated into an aqueous and an oil phase. Theaqueous phase is further sent to the nitropropane recovery column whichis operated at a pressure of 14.7 psi (1 atm) to recover the dissolvednitropropanes. Water, organic acids, and nitric acid are obtained as thebottom stream, whereas the top stream is cooled and decanted to obtainnitropropanes. Compared to the conventional scheme, the non-condensablestream is small and contains negligible amount of propane and2-nitropropane, thus eliminating the need for the tail-gas recoverycolumn.

The expected energy and capital requirement for a 2-nitropropaneproduction rate of 5065.25 lb/h is estimated for both a no-recyclescheme and an aqueous recycle scheme, and compared in Table 4. Theaqueous recycle option achieves almost similar 2-nitropropane recoveryin the oil stream with an energy savings of 4.3 MMBTU/h in thenitropropane recovery column and 2.12 MMBTU/h in the heat exchanger,allowing elimination of the tail gas recovery column. Moreover, asmaller size nitropropane recovery column is required in the aqueousrecycle scheme (2.1 ft. diameter) as compared to the conventional scheme(3.5 ft. diameter).

TABLE 4 Expected Energy and Capital requirement for aqueous recyclescheme as compared with the conventional scheme Aqueous No-recycleRecycle Scheme Scheme Absorber Equilibrium stages 10 11 Column dia. (ft)2.20 2.20 Pressure, atm 10.00 3.20 250 psig steam, lb/h 5930.00 5202.00Nitropropane Equilibrium stages 11 11 recovery Column dia. (ft) 3.5 2.2column Pressure, atm 1.3 1 Q_(reboiler), MMBTU/h 7.2 2.9 Tail-gasEquilibrium stages 8 — recovery Column dia. (ft) 1 — column Pressure,atm 1.1 — Heat No. of exchangers 2 4 exchanger Cooling duty, −4.4 −2.28MMBTU/h Compressor MMBTU/h 0.03 0.53 duty Recovered oil Water, lb/h 44.437.1 phase Nitrous oxide 2.3 1.8 composition Propane 107.3 73.5 Acetone117 114.4 Acetic acid 30.6 68.3 Butane 15.9 14.1 Nitromethane 61.6 61.7Nitroethane 41.5 41.5 Propionic acid 7.4 16.23 2-nitropropane 5062.85060.3 1-nitropropane 459.6 459.6 1-nitrobutane 0.4 0.4 2-nitrobutane1.6 1.6 2,2-dinitropropane 215.1 215.1 2-nitropropane 99.95% 99.90%recovery

Example 3 Propane Nitration with No Nitroparaffins in the Reactor Feed

Propane is reacted with 20 weight percent aqueous nitric acid with theabove described reactor at a reactor pressure of 1400 psi (96.7 atm), areaction temperature of 285° C., a residence time of 153 seconds, and apropane to nitric acid mole ratio of 1.81:1. The feed composition andthe reaction product stream composition are summarized in Table 5.

TABLE 5 Feed composition and reaction product stream compositionComponent Feed (g) Reaction Product (g) Propane 1185 769 Nitric Acid 93820.5 Water 3728 4287 Acetic Acid 0 110 Acetone 0 11.1 Nitromethane 0 6.1Nitroethane 0 4.3 2-nitropropane 0 491 1-nitropropane 0 752,2-dinitropropane 0 8.0 Nitric oxide 0 48.5 Nitrous oxide 0 5.6Nitrogen 0 12.7 Carbon monoxide 0 24.0 Carbon dioxide 0 221.7

Key performance metrics for this reaction are summarized in Table 6.

TABLE 6 Key performance metrics for nitration of propane with nonitroparaffins in the reactor feed Nitric acid conversion (%) 97.8Propane conversion (%) 35.1 Nitric acid yield 1.45 Propane yield 0.72Nitromethane selectivity (%) 1.1 Nitroethane selectivity (%) 0.71-nitropropane selectivity (%) 13.0 2-nitropropane selectivity (%) 85.22-nitropropane to 2,2-dinitropropane 61.5 weight ratio

Example 4 Propane Nitration with Nitroparaffins in the Reactor Feed

Propane is reacted with 20 weight percent aqueous nitric acid with theabove described reactor at a reactor pressure of 1400 psi (96.7 atm), areaction temperature of 285° C., a residence time of 153 seconds, and apropane to nitric acid mole ratio of 1.82:1. The feed composition andthe reaction product stream composition are summarized in Table 7.

TABLE 7 Feed composition and reaction product stream compositionComponent Feed (g) Reaction Product (g) Propane 1343 906 Nitric Acid1054 21.1 Water 3875 4447 Acetic Acid 144 249 Acetone 1.4 15.4Nitromethane 4.3 14.8 Nitroethane 1.0 6.5 2-nitropropane 49.3 5581-nitropropane 6.3 89 2,2-dinitropropane 0.3 8.8 Nitric oxide 0 43.5Nitrous oxide 0 6.9 Nitrogen 0 72.0 Carbon monoxide 0 16.4 Carbondioxide 0 28.1

Key performance metrics for this reaction are summarized in Table 8.

TABLE 8 Key performance metrics for nitration of propane withnitroparaffins in the reactor feed Nitric acid conversion (%) 98.0Propane conversion (%) 32.5 Nitric acid yield 1.55 Propane yield 0.71Nitromethane selectivity (%) 1.7 Nitroethane selectivity (%) 0.91-nitropropane selectivity (%) 13.3 2-nitropropane selectivity (%) 82.72-nitropropane to 2,2-dinitropropane 59.5 weight ratio

A comparison of Table 6 (no nitroparaffins in the reactor feed) withTable 8 (nitroparaffins in the reactor feed) shows that the weight ratioof 2-nitropropane to 2,2-dinitropropane does not significantly changewhen nitroparaffins are present in the reactor feed, as when an aqueousrecycle scheme is used. This indicates that 2-nitropropane in thereactor feed does not further react to form 2,2-dinitropropane to anyappreciable extent. The nitric acid and propane yields also do notchange (within measurement accuracy). Examples 3 and 4 illustrate thatthe presence of nitroparaffins in the reactor feed, as in an aqueousrecycle process, does not significantly affect the 2-nitropropaneselectivity.

While the invention has been described above according to its preferredembodiments, it can be modified within the spirit and scope of thisdisclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using the generalprinciples disclosed herein. Further, the application is intended tocover such departures from the present disclosure as come within theknown or customary practice in the art to which this invention pertainsand which fall within the limits of the following claims.

1. A process for synthesizing at least one nitroalkane, the processcomprising: reacting a hydrocarbon feedstock with aqueous nitric acid ina reactor at a reactor pressure and a reaction temperature, such that aproduct stream comprising nitrated compounds and byproducts is formed;separating the product stream into at least an oil phase, a gas phase,and an aqueous phase, wherein the oil phase and the aqueous phasecontain nitrated compounds; dividing the aqueous phase into a firstaqueous stream and a second aqueous stream; returning the first aqueousstream to the reactor; and recovering the at least one nitroalkane fromat least one of the oil phase and the second aqueous stream.
 2. Aprocess according to claim 1 further comprising: absorbing water-solubleand oil-soluble components from the gas phase to form a gas-recoveredmixture; separating a gas-recovered aqueous phase from the gas-recoveredmixture; and introducing the gas-recovered aqueous phase to a strippingapparatus to recover the at least one nitroalkane.
 3. A processaccording to claim 1 wherein between about 65 and 85 percent of theaqueous phase is divided into the first aqueous stream.
 4. A processaccording to claim 1 wherein the aqueous nitric acid is added to thereactor at a 10 to 50 weight percent solution.
 5. A process according toclaim 4 wherein the aqueous nitric acid is added to the reactor at a 15to 40 weight percent solution.
 6. A process according to claim 5 whereinthe aqueous nitric acid is added to the reactor at a 18 to 35 weightpercent solution.
 7. A process according to claim 1 wherein the molarratio of hydrocarbon to nitric acid is at least about 1.2:1.
 8. Aprocess according to claim 1 wherein the reactor pressure is at leastabout 1000 psi.
 9. A process according to claim 1 wherein the reactiontemperature is between about 215 and 325 degrees Celsius.
 10. A processaccording to claim 1 wherein the reaction temperature is greater than230 degrees Celsius.
 11. A process according to claim 1 wherein thereaction temperature is 290 degrees Celsius or less.
 12. A processaccording to claim 1 wherein the reactor is a downflow configuredreactor.
 13. A process according to claim 1 wherein the reactor is apacked reactor.
 14. A process according to claim 1 wherein the reactoris an un-packed reactor.
 15. The process according to claim 1, whereinthe at least one nitroalkane is 2-nitropropane.
 16. The processaccording to claim 1, wherein the at least one nitroalkane is2,2-nitropropane.
 17. A process for synthesizing at least onenitroalkane, the process comprising: reacting a hydrocarbon feedstockwith aqueous nitric acid in a reactor at a reactor pressure and areaction temperature, such that a product stream of nitrated compoundsand byproducts is formed; quenching the product stream to separate theproduct stream into at least an oil phase, a gas phase, and an aqueousphase; dividing the aqueous phase into a first aqueous stream and asecond aqueous stream; returning the first aqueous stream to thereactor; combining the oil phase, the gas phase, and the second aqueousstream in an absorber; absorbing water-soluble and oil-solublecomponents from the gas phase into the oil phase and the second aqueousstream to form a gas-recovered mixture; separating a gas-recoveredaqueous phase from the gas-recovered mixture; and recovering the atleast one nitroalkane from at least one of the oil phase and the secondaqueous stream.
 18. An apparatus for synthesizing at least onenitroalkane, the apparatus comprising: a reactor for reacting ahydrocarbon feedstock with aqueous nitric acid to produce a reactionproduct stream; a cooling system for quenching the reaction productstream such that it phase separates into at least a gas phase, an oilphase, and an aqueous phase; a divider for dividing the aqueous phaseinto a first aqueous stream and a second aqueous stream; a recyclingsystem for returning the first aqueous stream to the reactor; and arecovery system for recovering the at least one nitroalkane from atleast one of the oil phase and the second aqueous stream.
 19. Anapparatus according to claim 18, wherein the reactor the reactor is adownflow configured reactor.
 20. An apparatus according to claim 18,further comprising an absorber for absorbing water-soluble andoil-soluble components from the gas phase into the oil phase and thesecond aqueous stream to form a gas-recovered mixture.